Process and product for protecting aluminium, magnesium, zing and their alloys against corrosion



Patented Aug. 22, 1933 UNITED STATES PROCESS AND PRODUCT FOR PROTECTING ALUMINIUM, MAGNESIUM,

ZINC AND THEIR ALLOYS AGAINST CORROSION Pierre Prier, Clichy, France No Drawing. Application April 6, 1931, Serial No. 528,250, and in France April 24, 1930 6 Claims.

This invention has for object improvements in the process and product forming the subject-matter of the United States Patent application No. 401,38 In this patent application have been 5 set forth the conditions which are necessary and sufficient for causing a deposit to be made on the metals it is desired to protect.

The metals used for this protection are given by way of indication, viz: vanadium, molybdenum, tungsten, titanium, uranium, niobium, manganese and also chromium which as all the preceding metals possesses the required qualities and has in particular, the property of forming chromi'c salts and chromates.

Generally speaking, for protecting articles against corrosion, use was made of the action of an alkaline bath containing one of the alkaline salts of the most oxygenated oxide of a metal capable of forming at least two oxides, the most oxygenated being soluble in alkaline solutions and the less oxygenated not being soluble therein.

The present invention has particularly for object a process derived from the preceding one and having special advantages in that it is or great efiiciency and can be commercially carried out.

It has also for object a product serving to prepare the bath to be used for obtaining the required protecting deposit.

This product comprises in a mixture with the fixing product the main ingredient of which is vanadium, molybdenum, etc., an oxy-acid salt or an organic oxy-compound and an alkali phosphate and, preferably, a certain quantity of alkali carbonate, or of an alkali, or of another .basic salt, such for instance as cyanides of sodium or potassium.

By dissolving this product in water, a bath is obtained which, when brought to boiling point, will serve to treat articles made of aluminium, magnesium or zinc, or their alloys, on which a protecting deposit is to be formed.

It has been found that articles made of aluminium or aluminium alloy which are to be pro tected give rise in the active' bath according to the above mentioned patent application to a fiaky or fiocculent deposit of alumina soluble in the hot state in'the form of aluminate, which is decomposed by cooling.

' The formation of aluminium hydroxide hinders fixation by partially concealing the metal, this increasing the duration of the operation and giving a deposit which is insufiiciently homogeneous.

It has been found that for eliminating this alumina, the presence of oxy-acid salts or of organic oxy-compounds such as malic acid, tartaric acid, citric acid, sugar, starch, etc., or of an alkali phosphate, alone or to which is added a basic body such as alkali carbonate or alkali, is necessary.

It prevents the formation of alkaline aluminate either by reducing aluminium to the condition of soluble negative complexions in the case of oxycompounds, or by causing precipitation of a dense alumina phosphate insoluble in the hot state in the case of alkali phosphates.

Cpnsequently, the time necessary for the formation of the protecting layer is diminished, and the hor geneity of the latter, and therefore its resistance, are increased.

The bath can serve indefinitely by enriching it with a mixture composed of an active salt, an oxy-compound, an alkali phosphate and an alkali carbonate or an alkali.

The alkali content must remain proportional to the fixing salt content.

By way of example, the following proportion is suitable:

Per cent Phospho-chromate and sulpho-molybdate 1. 50 Tri-phosphate of sodium 0.40 Carbonate of sodium 1. Tartrate of sodium 1. 80

- Per cent Phospho-chromate and sulpho-molybdate 1. 50 Tri-phosphate of sodium 0.50 Carbonate of sodium 1. 20 Tartrate of sodium 1. 50

The above example is given by way of indication and is not to be considered as limitative.

The protecting layer formed constitutes an excellent fixing base for any varnish and paint.

What is claimed:

1. A process for protecting aluminium, magnesium, zinc and their alloys against corrosion, which consists in forming a protecting layer on articles made of these metals or alloys by the action of a hot bath containing in aqueous solution about 1.5% of a fixing salt, about 1.5% of an no alkaline salt of an organic oxy-acid, and about 0.5% of an ortho-phosphate of an alkali metal, the said, fixing salt consisting in an alkaline salt of the most oxygenated oxide of a metal capable of forming at least one o'xide soluble in an alkaline solution and a less oxygenated oxide insoluble in such a solution.

2. A process for protecting aluminium, magnesium, zinc and their alloys against corrosion, which consists in forming a protecting layer on articles made of these metals or alloys by the action of a hot bath containing in aqueous solution about 1.5% of both a phospho-chromate of an alkali metal and a 'sulpho-molybdate of an alkali metal, about 0.5% of an ortho-phosphate of an alkali metal and about 1.5% of an alkaline salt of an organic oxy-acid.

3. A process for protecting aluminium, magnesium, zinc and their alloys against corrosion, which consists in forming a protection layer on articles made of these .metals or alloys by the action of a hot bath containing in aqueous solution about 1.5% of both a phospho-chromate of an alkali metal and a sulpho-molybdate of an alkali metal, about 0.5% of an ortho-phosphate of an alkali metal, about 1.5% of a carbonate of an alkali metal and about 1.5% of an alkaline salt of an organic oxy-acid.-

4. A product adapted to be dissolved in water for the treatment of articles made of aluminium, magnesium, zinc and the like in order to protect them against corrosion, this product being constituted by a mixture comprising about 1.5% of a fixing salt, about 1.5% of an alkaline salt of an organic oxy-acid, and about 0.5% of a phosphate of an alkali-metal the said fixing salt consisting in an alkaline salt of the most oxygenated oxide of a metal capable of forming at least one oxide soluble in an alkaline solution and a less oxygenated oxide insoluble in such a solution.

5. A product adapted to be dissolved in water for the treatment of articles made of aluminium, magnesium, zinc and the like in order to protect them against corrosion, this product being constituted by amixture comprising about 1.5% of both a phospho-chromate of an alkali metal and a sulpho-molybdate of an alkali metal, about 0.5% of an ortho-phosphate of an alkali metal and about 1.5% of an alkaline salt of an organic oxy-acid.

6. A product adapted to be dissolved in water for the treatment of articles made of aluminium,

magnesium, zinc and the like in order to protect them against corrosion, this product being constituted by a mixture comprising about 1.5% of both a phospho-chromate of an alkali metal and a sulpho-molybdate of an alkali metal,-about 0.5% of an ortho-phosphate of an alkali metal, about 1.5% of a carbonate of an alkali metal and about 1.5% of an alkaline salt of an organic oxy-acid.

PIERRE PRIER. 

